The present invention relates generally to a heat treatment system for heat-treating a semiconductor wafer, such as a silicon substrate.
Generally, in order to produce a semiconductor integrated circuit, deposition, pattern etching, oxidation diffusion, annealing and so forth are repeated with respect to a silicon wafer, such as a semiconductor wafer, to form a large number of desired elements thereon.
For example, in the case of deposition, a semiconductor wafer is mounted on a supporting table in a processing vessel capable of being evacuated. This is heated by a heating means to a predetermined temperature to be maintained at the temperature. In addition, while a deposition gas is supplied into the processing vessel, the interior thereof is maintained in a predetermined reduced pressure atmosphere. Thus, a required thin film is deposited on the surface of the wafer. In this case, there are some cases where, if a certain kind of gas is used, deposition is carried out by producing plasma by a high-frequency voltage which is applied between top and bottom electrodes provided in the processing vessel.
By the way, there are recently some cases where metal films, such as Ti (titanium) films, W (tungsten) films, Ta (tantalum) films and Al (aluminum) films, and/or nitride films thereof are deposited since electric characteristics thereof are good. As raw material gases for use in deposition of films containing these metals or metal compounds, there are raw material gases having a very high vapor pressure, such as TiCl4 (titanium tetrachloride), PET (pentoethoxy tantalum) and DMAH (dimethyl aluminum hexide). If such a raw material gas having a high vapor pressure is used, it is in a gas state only at high temperatures, so that produced reaction by-products are easy to adhere to the inner wall faces and bottom face of the processing vessel, the temperature of which has a tendency to lower, thereby causing particles. In addition, on some process conditions, a portion of the processing vessel, such as the bottom of the processing vessel, conversely has a tendency to be in a over heating state to promote corrosion.
Therefore, in conventional single wafer heat treatment systems, a temperature control system, such as a heat transfer medium circulating system, is provided for running a heat transfer medium through a medium passage, which is provided in the side wall and/or bottom portion of a processing vessel, to control temperature so that the temperature of the side wall and bottom portion is within a predetermined allowable temperature range.
By the way, the above described temperature control system, such as the heat transfer medium circulating system, requires a tank for maintaining the heat transfer medium at a constant temperature. The structure of this tank is very complicated, and a heat insulating means must be also provided around the circulating passage in which the heat transfer medium is circulated. Therefore, there are problems in that the whole system is not only very large to require a very large space, but costs and power consumption increase very much.
In addition, since a rolling mechanism, such as a compressor, for controlling the temperature of the heat transfer medium is used, it is required to periodically carry out maintenance. Moreover, as the heat transfer medium usually used herein, there are Galden (trade name) and Fluorinert (trade name) having a high vapor pressure in view of thermal efficiency and so forth. However, there is also a problem in that, if Galden and Fluorinert leak, they cause contamination having a serious bad influence in the production of a semiconductor integrated circuit.
The present invention has been made in order to effectively solve the above described problems. It is an object of the present invention to provide a heat treatment system, which is not only capable of appropriately controlling the temperature in a processing vessel, but also capable of reducing space and energy, by combining a resistive heating means with a thermoelectric conversion means.
According to the present invention, a heat treatment system comprises: a cylindrical processing vessel; a supporting table, raised by a support from a bottom portion of the processing vessel, for mounting thereon an object to be processed; processing object heating means, provided in the supporting table, for heating the object to be processed; thermoelectric conversion means which is provided in the bottom portion of the processing vessel and which is capable of selectively heating and cooling; resistive heating means provided in a side wall of the processing vessel; and a temperature control part for controlling operations of the thermoelectric conversion means and the resistive heating means.
Thus, the bottom portion of the vessel which must be heated or cooled in accordance with process conditions is selectively heated or cooled by the thermoelectric conversion means if necessary, and the side wall of the vessel which has a tendency to have a lower temperature than that of the bottom portion of the vessel during process to allow reaction by-products from adhering thereto is always heated by the resistive heating means, so that it is not only possible to control the processing vessel at an appropriate temperature, but it is also possible to minimize the whole system to reduce the space and energy.
In addition, since it is not required to provide any rolling mechanisms, it is possible to greatly improve maintenance performance in comparison with the temperature control system, such as the heat transfer medium circulator, which has been conventionally used.
In this case, the thermoelectric conversion means is preferably provided with a thermal conversion plate in which a medium passage for running a heat transfer medium to discard undesired heat and cold is formed. In addition, the thermal conversion plate is preferably provided on the side of a bottom face of the thermoelectric conversion means.
The bottom portion of the processing vessel may be provided with temperature measuring means for measuring a temperature of the bottom portion of the processing vessel, and the temperature control part may carry out a temperature control operation on the basis of a measured value of the temperature measuring means.
The temperature control part may measure the temperature of the bottom portion of the processing vessel on the basis of a voltage due to the Seebeck effect of the thermoelectric conversion means, and carry out a temperature control operation on the basis of a measured value of the temperature of the bottom portion of the processing vessel. Thus, it is not required to provide any temperature measuring means, such as a thermocouple.
The thermoelectric conversion means may include a Peltier device.
The thermoelectric conversion means may be provided with a thermal conversion plate in which a medium passage for running a heat transfer medium to discard undesired heat and cold is formed, and the Peltier device may be provided between the bottom portion of the processing vessel and the thermal conversion plate. The Peltier device may be bonded to the thermal conversion plate.
The resistive heating means may comprise a plurality of rod-shaped cartridge heaters. The cartridge heaters may be buried in the side wall of the processing vessel so as to extend in vertical directions.